In a previously known valve timing control apparatus, an inner rotor, which is rotated in a circumferential direction synchronously with the camshaft, is rotated relative to an outer rotor, which is rotated in the circumferential direction synchronously with the crankshaft, so that the valve timing is adjusted in response to rotational phase between the inner rotor and the outer rotor.
For instance, JP2005-155346A (corresponding to US2005/0115528A1) discloses one such a valve timing control apparatus that has the outer rotor, which includes a synchronously rotatable member, a stopper member and a positioning member. Specifically, the synchronously rotatable member is rotated synchronously with the crankshaft when the synchronously rotatable member receives the crank torque. The stopper member is joined to the synchronously rotatable member in the axial direction and is thereby rotated synchronously with the synchronously rotatable member. The stopper member stops rotation of the inner rotor that is rotated relative to the stopper member in the circumferential direction. The positioning member is shaped into a rod form and extends in the axial direction. The positioning member positions the stopper member relative to the synchronously rotatable member in the circumferential direction.
In the valve timing control apparatus of JP2005-155346A (corresponding to US2005/0115528A1), the positioning member functions such that the positioning member limits positional deviation of the stopper member relative to the synchronously rotatable member, which receives the crank torque, when the stopper member stops the rotation of the inner rotor. Here, a shaft portion of the positioning member, which extends straight, is press fitted into a press fitting hole portion of the stopper member, which extends straight. Furthermore, a distal end portion of the positioning member projects into a tapered hole portion of the synchronously rotatable member, which has an inner peripheral surface tapered to have an inner diameter that is progressively increased in the axial direction toward the stopper member. The distal end portion of the positioning member, which projects into the tapered hole portion of the synchronously rotatable member, contacts the inner peripheral surface of the tapered hole portion at a specific side in the circumferential direction. The press fitting configuration and the contacting configuration described above can guarantee positioning of the stopper member relative to the synchronously rotatable member in a manner that absorbs positional deviation of the central axis of the press fitting hole portion and the central axis of the tapered hole portion from its normal position (a specified position) and further guarantee the accuracy of the positioning of the inner rotor at the time of stopping the rotation of the inner rotor regardless of manufacturing tolerance.
However, in the valve timing control apparatus of JP2005-155346A (corresponding to US2005/0115528A1), the positioning member projects from the press fitting hole portion of the stopper member toward the tapered hole portion side. Therefore, at the time of inserting a distal end part of the shaft portion of the positioning member into the tapered hole portion upon press fitting of the shaft portion of the positioning member into the hole portion to form the positioning structure, the shaft portion tends to be caught by the tapered hole portion side edge of the press fitting hole portion. In such a case, as indicated by a solid line in FIG. 14A, a stick-slip phenomenon (also referred to as a slip-stick phenomenon) occurs in a period T, which is from the time of projecting the shaft portion from the press fitting hole portion to the time of contacting the distal end part against the inner peripheral surface of the tapered hole portion at the specific side. The stick-slip phenomenon is a phenomenon of self-oscillation of the positioning member that involves repeat of a moving state (slipping state), which is governed by a small kinetic frictional force between the shaft portion and the press fitting hole portion, and a stop state (sticking state), which is governed by a large kinetic frictional force between the shaft portion and the edge.
When the stick-slip phenomenon of the positioning member occurs, control of a press-in load (also referred to as a press-fit load) applied to the positioning member to insert the positioning member into the press fitting hole portion becomes difficult at the time of contacting of the distal end part of the positioning member against the tapered hole portion. Therefore, in such a case, the press-in load, which is applied to the positioning member, may become excessively large to cause deformation of the synchronously rotatable member. Here, the deformation of the synchronously rotatable member of the outer rotor, which is rotated by the crank torque transmitted from the crankshaft, has an influence on the adjustment accuracy of the valve timing in accordance with the rotational phase between the outer rotor and the inner rotor. Therefore, it is necessary to limit the deformation of the synchronously rotatable member.